How to solve infrastructure dilemmas?

The choice of infrastructure is one of the most frequent debates about public transport: whether to build a rail-based line (heavy rail, light rail and anything in between) or expand a bus service with costs and benefits of each option. The best possible answer, in short, is: it all depends on the particular circumstances, mainly the goals, major constraints (“What can go wrong and why?”) and the budget.

The following analysis compares 6 modes of transport across 6 parameters and it is intended to help when making a decision about the development of a transport network. It assumes a perspective of an average European mid- to large-size city that already has some but not all of the modes listed and likewise it some infrastructure, most likely fragmented. (I am concentrating on high capacity modes of transport that are at least to some extent independent from other traffic.)

The conclusions are summarised in a table below:

Individual parameters:

Costs of new infrastructure:

Tram or light rail (an additional line) – medium: new infrastructure (line extension or a link) added to the existing one

BRT – medium: new infrastructure (a street with dedicated lanes) added to the existing one

Commuter rail – none: maximising the use of existing infrastructure by modifying train routes on existing lines and adjusting the frequency *

Tram-train – small: merging the existing infrastructure into a single network by building links between train and tram lines

Premetro – high: new infrastructure (a city centre tram tunnel) added to the existing one

Metro – very high: new infrastructure independent of the existing one

Costs of new vehicles:

Tram or light rail (an additional line) – medium: using existing fleet with some purchases (to maintain the frequency on the existing network)

BRT – medium: a completely new fleet needed, in order achieve a higher capacity than regular buses

Commuter rail – none: maximising the use of existing fleet *

Tram-train – high: a completely new fleet needed

Premetro – medium: using existing fleet with some purchases (to avail of a higher network capacity)

Tram-train – small: direct routes from suburban areas to the city centre

Premetro – small: many direct routes

Metro – large: each line has typically only one possible route

* The descriptions above refer to a start of commuter rail operations. Serving additional areas and increasing frequency requires large costs related to e.g. building a new line or adding additional tracks in the city centre (in order to avoid track sharing with long-distance trains).

** A speed comparable with rail-based transport requires dedicated lanes on the entire route. A compromise of partial routing outside of dedicated lanes (e.g. in the city centre) creates a risk of a noticeable drop in speed and BRT buses getting caught in traffic jams.